I was able to get the new shed foundation in place this weekend. Below is a set of photos showing the process.
I have never used pier blocks before, but everything worked out OK. In the past, I have always nailed the metal supports to the posts & beams and then poured concrete. The method here is very similar, you just need to make sure the bottom of the holes are level and the right height. After doing it, I think I still would have preferred the old way, but these are the materials I harvested from the old shed.
Here is the first beam - 16' feet long - set into place with four pier blocks. This is the highest ground area, so I made the holes as deep as the blocks.
A tip: I over-dug the holes by 1" to 2", then I poured dry concrete mix into the hole to get the bottom to the right height. This makes it easy to get it flat and level. Also, the powdery texture of the dry mix allowed me to move the block around a bit by tapping them gently with a small sledge hammer. Once in place, I tamped dirt around them. Once everything is set, I just spray the block with a hose and they are set solid.
Here is the second beam, which was leveled and squared to the first. I needed to buy new 16' long beams, but I will also be able to use the 6' ones from the old shed. They form the joist on the outer edge as shown, plus those that will be under where the lawn tractor will sit. I figure 4x4's on 16" centers are not going to sag with a 6 ft' span, even with a couple hundred pound mower sitting on them most of the time.
As I moved down the slope, I needed to add small post pieces under the beams. I toe-nailed them in, then completed attaching them with a 7" gutter screw and polyurethane glue. I spread the glue all over the surface of the post ends to seal them from water. I don't expect water to get in there, but its a very simple and cheap precaution.
The picture below shows the third (and last) beam in place, along with joists on the ends and in the center. This set-up allowed me to do the final squaring and leveling of the foundation. I used the asphalt shingles shown to make final adjustments up to level. When in doubt, I set posts & piers about 1/8" short, so I can shim them to get right on to level. The shingle never compresses, and it's used to level full size houses.
I like to take my time with this step and ideally come back the following day to verify everything is correct. The more level and square it is, the easier the rest of the construction will go, and the better it will look.
Here I have added the rim joist so I can easily add the rest of the cross-joists. This will get covered up by the cedar siding and a drip-edge. The cross-joists are cut from the studs and rafters of the old shed.
Once the joist are down, I will put 3/4 plywood down as the deck and start framing the walls.